The present invention relates to the thermal recovery of heavy crude oils and particularly to the steam generators used for supplying steam for thermal recovery projects. The conventional steam generator used in a thermal recovery project comprises a radiant section followed by a convection section which joins with the stack for the exhaust gases. The radiant section consists of a cylindrical furnace having an outer shell lined with a plurality of boiler tubes. The furnace burner is placed at one end of the cylindrical furnace and the combustion products flow through the radiant section into the convection section of the steam generator and out the stack. The boiler tubes lining the radiant section are arranged in a once-through flow pattern wherein the water is introduced through one of the tubes, flows through all of the tubes and then exits from the tube adjacent the inlet.
In the above described generator the tubes of the radiant section are secured to the outer shell by means of tube hangers. These tube hangers comprise a yoke section which is provided with openings for supporting the tubes with the yoke section being attached to a supporting leg that is firmly anchored to the outer shell.
While the above tube hangers adequately support the tubes in the radiant section of the steam generator, they create unnecessary difficulties when it is necessary to replace a tube or a tube hanger. The inner surface of the yoke member of the tube hanger is exposed to the direct radiant heat of the furnace causing this portion of the hanger to fail. If a tube hanger fails, it is of course, necessary to remove all of the tubes in the tube hanger and the hanger itself in order to replace the hanger. The same problem occurs when it is necessary to remove and replace one of the tubes. It is normally impossible to slide the tubes out of the hanger from one end of the generator since the radiant heat tends to warp the tubes causing them to stick in the hangers. The removal of the hangers is a difficult job since they are normally welded to the outer shell of the steam generator.